1. Field of the Invention
The present invention relates to an electric connecting anisotropic conductive material used for bonding and connecting fine electrodes of a LSI chip or another to electrodes formed on a wiring package substrate. The present invention also relates to a method for connecting and bonding an element such as LSI chip onto a wiring package substrate, by using the anisotropic conductive material.
2. Description of Related Art
In the prior art, this type of electric connecting anisotropic conductive material has been formed of conductive particles dispersed in an insulative bonding agent. Connection has been achieved by a heat press bonding performed under a pressure of 20 Kg/cm.sup.2 to 30 Kg/cm.sup.2 at a temperature of 180.degree. C. to 200.degree. C. For example, the conductive particles have been formed of solder particles or particles formed of a macromolecular material such as divinylbenzene copolymer and having a surface coated with a conductive metal thin film of Au, Ni, etc. The conductive particles have an averaged particle size of 0.01 .mu.m to 50 .mu.m. The insulative bonding agent has been formed of, for example, a thermoplastic resin such as urethanes or styrene-butadiene-styrene type block copolymers. Alternatively, a thermosetting resin of epoxy type or others has been used. The anisotropic conductive material is dispersed in the insulative bonding resin with a proportion of 1% by volume to 10% by volume.
In addition, in a conventional packaging method, an LSI chip formed with electrode pads and a wiring substrate formed with electrode terminals in correspondence to the electrode pads are located to oppose to each other, with a hot-melt adhesive resin containing conductive particles dispersed therein being interposed between the LSI chip and the wiring substrate. Thereafter, the LSI chip is depressed onto the wiring substrate, and the whole is heated, so that the hot-melt adhesive resin is softened, and the electrode pads and the corresponding electrode terminals are electrically connected through the conductive particles.
In the above mentioned conventional connecting and bonding method, if the amount of the conductive particles for electrically connecting between the electrode pads and the corresponding electrode terminals becomes much, a short-circuit or a current leakage will occur between adjacent electrode pads and between adjacent electrodes. In order to avoid this problem, if the amount of the conductive particles is reduced, a connection resistance will not only increase but also vary. In ultimate cases, the electrode pads and the corresponding electrode terminals to be connected to each other remain in an electrically opened condition. This is a serious defect which will cause a malfunction of the devices. In addition, this inclination will become remarkable more and more with a recent microminiaturization of connection sizes.